Heart is a tyrannosaurus who is found and raised bv a herbivore mother. After learning his true nature as a meat eater, he runs away from home and finds a baby ankylosaurus egg that hatches and thinks Heart is his father. After accidentally naming the baby Yummie - thinking he looked tasty - their love for one another tests the bounds of nature vs. nurture.

Two sisters move to the country with their father in order to be closer to their hospitalized mother, and discover the surrounding trees are inhabited by Totoros, magical spirits of the forest. When the youngest runs away from home, the older sister seeks help from the spirits to find her.